Trellis coded modulation is a combination of convolutional coding and modulation. A convolutional code, or trellis code, is an error-correcting code in which each m-bit information symbol to be encoded is transformed into an n-bit symbol. These n bits are modulated, that is converted to analog form via a sinusoidal carrier, and transmitted. In trellis coded modulation, the coding and modulation are combined in one function.